1. Field of the Invention
The present invention relates generally to an exhaust manifold for an internal combustion engine provided with a turbocharger, and more particularly to an exhaust manifold connecting between a trubocharger and the cylinder head of a four-cylinder in-line internal combustion engine.
2. Description of the Prior Art
A dynamic-pressure-type turbocharger is often used in an internal combustion automotive engine, in which the volume of a pipe leading exhaust gas from the engine to a turbine is designed as small as possible to effectively utilize the dynamic energy of the exhaust gas.
When a dynamic-pressure turbocharger of the aforesaid type is used in a multicylinder in-line internal combustion engine, exhaust gas emitted from each cylinder is simply collected in an exhaust manifold leading into a turbine. Since one exhaust stroke for one engine cylinder often overlaps with the exhaust stroke of another engine cylinder, the inner pressure within the exhaust pipe inevitably increases. Additionally, when an exhaust stroke overlaps an intake stroke, the pressure of discharging exhaust gas is reduced markedly, adversely effecting engine combustion efficiency. The above probldm is called exhaustion interference.
To overcome the aforsaid problems in an exhaust manifold connecting the cylinder head to the turbocharger in a four cylinder in-line engine, for example, where the firing sequence of the cylinders can be No. 1, No. 3, No. 4 and No. 2 or No. 1, No. 2, No. 4 and No. 3, the exhaust ducts communicating with cylinders No. 1 and No. 4 are disposed separately from those communicating with cylinder No. 2 and No. 3 to avoid exhaustion interference, i.e., alternating cylinders in the firing sequence can be connected without exhaustion interference.
In the prior-art exhaust manifold, however, since the length of one exhaust gas duct from one cylinder is not equal to that of another exhaust gas duct from another cylinder, it is impossible to accurately utilize the cyclic variation of exhaust gas pressure to pressure tune the turbine in the turbocharger.
The representative prior-art exhaust manifold for an internal combustion engine with a turbocharger will be described in more detail hereinafter with reference to FIGS. 1, 2 and 3.